The present invention relates to a vehicle radio communication system for performing radio communication between a vehicle and a structure through which the vehicle passes to identify the vehicle and, more particularly, to a vehicle identification system using radio wave arrival angle measurement for specifying a vehicle on the basis of the arrival angle of a radio wave transmitted from the vehicle.
As one of radio communication systems, there is an ETC (Electronic Toll Collection) system which charges vehicles for use of a toll road by radio communication. The ETC system is constituted by a first radio communication unit and electronic payment means (e.g., an IC card) mounted on a vehicle, and a second radio communication unit set at the toll gate (gate) of a toll road to communicate with the first radio communication unit.
In such an ETC system, the toll of the toll road is collected upon radio communication from the gate to the vehicle when the vehicle passes through the gate. More specifically, the toll is paid from the electronic payment means of the vehicle upon charging processing by radio communication from the gate.
Vehicles passing through the gate include vehicles compatible with ETC (to be referred to as ETC vehicles hereinafter) and vehicles incompatible with ETC (to be referred to as non-ETC vehicles hereinafter). When a lane dedicated to ETC vehicles or a lane for both ETC and non-ETC vehicles is set at the gate, the operator at the gate can collect the toll without contacting the drivers of the ETC vehicles.
According to this ETC system, the toll of the toll road can be collected without stopping vehicles at the gate. With this system, economical loss due to traffic delay can be avoided, convenience for users can be improved, and the labor in charging operation can be decreased.
The above-described conventional ETC system will be described with reference to FIGS. 14 and 15.
Referring to FIGS. 14 and 15, when an ETC vehicle 142 enters a communication setting area A of a radio communication antenna 121, which is set at the gate, communication for ETC (to be referred to as ETC communication hereinafter) is established between the radio communication unit at the gate and a radio communication unit 141 of the ETC vehicle 142.
However, when a non-ETC vehicle (not shown) enters a lane dedicated for the ETC vehicles 142 or a lane for both ETC vehicles and non-ETC vehicles, communication with the non-ETC vehicle is not performed. In this case, "stop" is turned on at an indicator 105 to stop the non-ETC vehicle.
If the gate is at the entrance of the toll road, a ticketing machine 151 issues a ticket. If the gate is at the exit of the toll road, the clerk in a tollbooth 152 collects the toll. For a vehicle in violation of the stop instruction, the number or driver of the vehicle is photographed, and the driver is charged later.
The communication setting area A where communication for ETC is done is set in the range of several meters in front of the radio communication antenna 121 so that a plurality of vehicles are hardly simultaneously present in the area. However, since the communication channel is designed in consideration of the system margin, and limitations are imposed on beam shaping by the radio communication antenna 121, communication is sometimes established even outside the communication setting area A. The area where ETC communication is established will be referred to as a communication enabled area B.
The communication enabled area B is wider than the communication setting area A, and a plurality of vehicles can easily simultaneously enter the communication enabled area B. As shown in FIGS. 14 and 15, the ETC vehicle 142 following a non-ETC vehicle 144 may enter the gate, and the non-ETC vehicle 144 and the ETC vehicle 142 may simultaneously present in the communication enabled area B.
In this case, ETC communication is established not with the preceding non-ETC vehicle 144 but with the ETC vehicle 142 following the non-ETC vehicle 144. However, since the vehicle which has transmitted the ETC communication signal cannot be specified, the gate side misunderstands that the ETC procedure with the non-ETC vehicle 144 is ended and allows the non-ETC vehicle 144 to pass. In fact, the non-ETC vehicle 144 is not charged, so reliable toll collection processing cannot be performed.